Amplifying or rectifying device



April 6, 1937.

Filed Feb. 4, 1935 INVENTORS POP/(0 .19. OY/fSTERHU/S JACOB I44 Z007IVATTORNEY Patented Apr. 6, 1937 UNITED STATES PATENT DFFUJE AMPLIFYING ORRECTIFYING DEVICE Delaware Application February 4, 1935, Serial No.4,800 In Germany March 15, 1934 4 Claims.

This invention relates to a circuit arrangement for amplifying and/orrectifying electrical high frequency oscillations in which dampingreduction by back coupling is used.

If in a receiving arrangement with a back coupling acting on the antennacircuit, the damping reduction caused by said backcoupling has such avalue that high frequency oscillations are produced, the latter will beemitted by the antenna and will consequently give rise to disturbinginterferences in other neighboring receivers.

It has been sought to avoid this draw-back by introducing the dampingreduction not in the antenna circuit, but in another tuned circuit ofthe receiver by using a back coupling, this circuit being coupled withthe antenna circuit through one or more amplifying tubes. This solutiongives satisfactory results if either the amplifying tube(s) interposedbetween the circuit whose damping is reduced and the antenna circuit is(are) furnished with a screen grid, so that the reaction across theanode control grid capacity of the tube may substantially be neglected,or the anode control grid capacity is neutralized in another knownmanner.

The same result may be achieved by the ar rangement according to ourinvention without, however, the interposition of an additional tubebeing necessary.

According to the invention the electrical high frequency oscillations tobe amplified or rectified are supplied to one of the grids (controlgrid) of a thermionic discharge tube having at least three grids, animpedance being inserted in the circuit connected to another gridseparated by a screened grid from the control grid, which impedance iscoupled with an impedance inserted in the anode circuit or with animpedance interposed in the circuit of another grid which is alsoseparated from the control grid by a screened grid, in such a mannerthat damping reduction by back coupling occurs in the last mentionedcircuit or in the anode circuit.

For a better understanding of the invention reference is made to theaccompanying drawing in which:

Figure 1 is a schematic circuit diagram of a regenerative detectorembodying the invention, and

Figure 2 is a circuit diagram of a similar detector in which capacitivefeedback is utilized.

The electron discharge tube I shown in Figure 1 comprises a directly orindirectly heated cathode 2, four grids 3, 4, 5 and 6 and an anode 1.The 5 control grid 3 of this tube is connected on the one hand through acondenser 8 to an antenna 9 and on the other hand through a resistanceIt] to the end of a grid bias resistance l l remote from the cathode,which resistance is bridged by a condenser l2. The direct voltage dropoccurring across the resistance l I supplies in a known manner thenegative bias for the control grid. Both of the grids 4 and 5 succeedingthe control grid have a constant positive potential with respect to thecathode and at least one of these grids is designed as a screen grid sothat a reaction of the grid 6 and of the anode 1 on the control grid 3is avoided. The grid 6 is connected-through a resistance I3 to thecathode 2, so that the direct current potential of this electrodecorresponds to that of the cathode. Furthermore the circuit connected tothe grid 6 comprises an oscillatory circuit M which is connected inseries with a condenser l5 and is tuned to the frequency of theoscillations to be received. Finally the anode circuit of the tube isconstituted by a reaction coil l6 inductively coupled with the coil 30of tuned circuit I4. This coil is connected in series with the primarywinding 3| of a low frequency transformer I! which is short circuitedfor high frequency currents by a condenser l8, the secondary of I! beingconnected to a pair of output terminals 32.

The operation of this arrangement is as follows:

The high or radio frequency oscillations re ceived by the antennacontrol the grid 3 and consequently a high frequency alternating currentwill flow in the circuit connected to the anode I. This current sets upa high frequency alternating voltage at the grid 6 owing to the couplingof the coil It with the tuned circuit M, which voltage is rectified inthe same manner as with grid rectification and causes a low frequencyvoltage drop across the resistance IS in accordance with the modulationof the received high frequency oscillations. This low frequency voltageset up at the grid 6 controls the anode current traversing the primarywinding of the low frequency transformer, so that the low frequencyoscillations may be reproduced, for instance, in a loudspeaker ortelephone connected through the secondary winding, if desired with theinterposition of a low frequency amplifier.

If the coupling between the coil l6 and coil 3B of the circuit I 4 ismade so close that the damping of the circuit connected to the grid 6becomes zero or negative, then high frequency oscillations are produced.

However, owing to the presence of the grids 4 and 5, at least one ofwhich is a screen grid as has been set out before, said oscillations donot cause any voltage variations in the control grid 3 circuit thusavoiding antenna radiation and incidental disturbances of neighboringreceivers due to interference. V

Figure 2 shows another circuit arrangement which substantiallycorresponds to that represented in Figure l and in which correspondingparts are denoted by similar numerals, but in Figure 2 a capacitativeback coupling is used between the third and fourth grids (5 and 6) whichback coupling may. be controlled by the variable condenser [9. The radiofrequency choke coil 33 is connected between grid 5 and the positivepotential source.

It will be appreciated that although in the circuit arrangements abovereferred to tubes having four grids are shown, the invention is notlimited thereto but also includes the use of tubes having three, five orsix grids, provided the control grid be separated from the other ones byat least one screened grids Furthermore it is obvious that the inventionalso applies to arrangements designed only for high frequencyamplification of the applied signal voltage.

What we claim is:

1. In a device of the classdescribed, the combination' of a thermionictube having a cathode, a signal control grid, a screen grid, a thirdgrid and a plate arranged in the order named, a circuitv connecting saidcathode and signal control grid including a resistor and means forbiasing said control grid negative with reference to said cathode, meansfor impressing a modulated radio frequency signal voltage on said signalcontrol grid, means for applying a steady positive voltage to saidscreen grid, a circuit connecting said third grid and cathode includinga portion resonant to the incoming signal frequency, and a circuitconnected to said plate including a feedback connectio-n to said lastnamed circuit and means for applying a positive potential to said plate.

2. The combination defined in the preceding claim in which a resistor isdirectly connected between said third grid and cathode.

3. In a device of the class described, the combination of a vacuum tubehaving acathode, a signal control grid, a screen grid, a third grid, afourth grid and a plate arranged in the order named, a circuitconnecting said cathode and signal control grid including a resistor,means for impressing a modulated radio frequency signal voltage on saidsignal control grid, means for applying a steady positive voltage tosaid screen grid, a circuit connecting said third grid and cathodeincluding a coil and condenser connected in parallel and resonant to theincoming signal frequency, a capacity connected between said third andfourth grids and an audio frequency output circuit connected tosaidplate.

4. In a device of the class described, the comv bination of a thermionictube having a cathode, a signal control grid, a screen grid, a firstcold electrode and a second cold electrode arranged in the order named,a circuit connecting said cathode and signal control grid including aresistor and means for biasing said control grid negative with referenceto said cathode, means for impressing signal voltage variations of adesired frequency on said signal control grid, a parallel resonantcircuit tunable to the desired signal frequency having one end connectedto said first cold electrode and its other end to the lower end of saidresistor, means for causing oscillatory currents to flow in saidparallel resonant circuit, means for impressing a substantially constantpositive potential on said screen grid and an audio frequency outputcircuit connected to said second cold electrode.

' POPKO REINDER DYKSTERHUIS.

JACOB VAN SLOOTEN.

